Front pillars that are to be disposed on the sides of a front portion of a vehicle cabin each have a closed cross section structure extending over substantially the entire area of the front pillar in a longitudinal direction, and this enables each of the front pillars to obtain a sufficient rigidity for a load that is input from the outside. However, in the case where a large impact load is input from the outside, it is impossible to completely eliminate deformation of such front pillars. Therefore, a vehicle body side structure capable of suppressing entry of deformed front pillars into a vehicle cabin by controlling the deformation behavior of each portion of the front pillars has been proposed (see, for example, Japanese Unexamined Patent Application Publication Nos. 2000-302058 and 2010-188983).
In the vehicle body side structure described in Japanese Unexamined Patent Application Publication No. 2000-302058, an inclined region of each of front pillars extending diagonally rearward and upward from a front end portion of each of the front pillars toward a corresponding one of roof side rails has a closed cross section structure, and a reinforcing member that is to be disposed in the closed cross section of each of the inclined regions includes a front reinforcing member and a rear reinforcing member. In an area outside a vehicle cabin, the front reinforcing member and the rear reinforcing member are superposed with each other in such a manner as to form a high-strength portion, and in an area inside the vehicle cabin, the front reinforcing member and the rear reinforcing member are separated from each other in such a manner as to form a fragile portion.
In the case of the above vehicle body side structure, when a large impact load is input from a front portion or side portions of a vehicle body, the inclined region of each of the front pillars is bent and deformed toward an area outside the vehicle cabin with the corresponding fragile portion acting as a bending center.
However, in the vehicle body side structure described in Japanese Unexamined Patent Application Publication No. 2000-302058, for example, in the case where a large impact load is input to a front region of one of the front pillars from diagonally from the front with respect to the lateral direction of the vehicle body, a situation may be assumed in which the inclined region of the front pillar is bent and deformed toward the area outside the vehicle cabin with the corresponding fragile portion acting as a center, and in which a moment oriented toward the inside of the vehicle cabin acts in a region extending from the front pillar to the corresponding roof side rail. Therefore, in the vehicle body side structure described in Japanese Unexamined Patent Application Publication No. 2000-302058, an additional reinforcement is required in order to prevent the roof side rails from entering the inside of the vehicle cabin to a large extent.